The proposed project consists of a continuing study of the effects of alterations in polycyclic hydrocarbon hydroxylase activity on carcinogenesis resulting from polycyclic hydrocarbon carcinogens and also of factors which effect the level of activity of these hydroxylases. There are three parts to the proposed investigation. The first is a histochemical and quantitative investigation of benzpyrene hydroxylase activity in tissues of mice subjected to chronic exposures to benzpyrene. Sequential studies of the activity of this enzyme system will be carried out in order to determine: (1) at what stage during the course of carcinogenesis the loss of activity found in neoplasms resulting from such exposures occurs; (2) whether the loss is focal or general; (3) whether it can be prevented or reversed and (4) its relationship to subsequent events. The second part of the proposed project is a study of the effects of induction of increased polycyclic hydrocarbon hydroxylase activity on carcinogenesis resulting from chronic exposures to low doses of polycyclic hydrocarbon carcinogens. The third part is an effort at identification of dietary factors which alter or control polycyclic hydrocarbon hydroxylase activity, to ascertain the relationship between the quantitative intake of such factors and polycyclic hydrocarbon hydroxylase activity, and to determine whether alteration in the dietary intake of such factors can change the neoplastic response to polycyclic hydrocarbon carcinogens.